Hi all,
do you know if there exists and where could I find an integrated (or small) power amplifier for signals around 700kHz?
I am using a very big/heavy one for a prototype but I want to miniaturize my circuit.
Thank you
Can you specify power and voltage?
Otherwise, APEX makes power amplifiers.
first of all thank you.
I am working with voltage values varying from 1V peak-to-peak up to 2V peak-to-peak. I have no idea what values I can expect in output of such a small amplifier. Tents? hundreds of the input value?
output voltage is meaningless unless you specify the load. a 74HC device will do 5Vp-p easily but that's probably not what you're looking for.
We can't help you without more information.
the load varies between 500\$\Omega\$ and 2k\$\Omega\$... let's say 1.5 k\$\Omega\$ is a good value
probably 100x voltage gain is a little too high, but around 40-50 would be better, and probably easier to find (?). Also the cost is not a problem
probably 100x voltage gain is a little too high, but around 40-50 would be better, and probably easier to find (?). Also the cost is not a problem
You can easily reduce the requirements, if you add a preamplifier to the circuit. Just have a general purpose opamp amplify the 1V signal by 10-15, running from a +/-15V supply, so the power amplifier does not need to be that accurate (offset) or optimize the bandwidth or anything like that.
Your stated requirements of 50-100V PP, 700kHz, 1.5Kohm don't really make sense.
At 700kHz, a capacitance of 200pF has a reactance of 1.1Kohm. There aren't many real loads that can tolerate 50V+ and have capacitance that low.
What kind of load are you driving?
What is your actual load voltage requirement?
thank you edavid. I am driving a small piezoelectric transducer (PZT) for ultrasounds. I am trying to drive it with a high voltage value because I have a high attenuation of the ultrasonic signal
So basically I have a signal generator to drive the PZT, bust since the maximum amplitude of the signals that my generator supports is too small I need to amplify it before applying it to the PZT.
I know that the PZT has a resistance R=1.5k\$\Omega\$
I know that the PZT has a resistance R=1.5k\$\Omega\$
That is unlikely. A PZT is almost a pure capacitance.
Pzts are a complex load that changes with load
thank you edavid. I am driving a small piezoelectric transducer (PZT) for ultrasounds.
What kind of signal? If it can be semi-square wave you can simply use
totem poles.
What kind of signal? If it can be semi-square wave you can simply use
totem poles.
[/quote]
just a sinusoid
I know that the PZT has a resistance R=1.5k\$\Omega\$
That is unlikely. A PZT is almost a pure capacitance.
Than I must be wrong, sorry. This is what I have, I thought that real was the internal resistance
Why not use a transformer?
just a sinusoid
The sonic output will be sinusoid any way, it's a pretty good filter.
Why not use a transformer?
because they are too bulky (?)
I know that the PZT has a resistance R=1.5k\$\Omega\$
That is unlikely. A PZT is almost a pure capacitance.
Than I must be wrong, sorry. This is what I have, I thought that real was the internal resistance
No that verical axis is Z the impedance, mostly due to capacitance reactance, not a DC resistance.
No that verical axis is Z the impedance, mostly due to capacitance reactance, not a DC resistance.
Ok, so from my figure, which is value of the load do I have to consider to evaluate the power that I am transferring to the PZT?
It looks like you need a resonant driver to make it work.
It looks like you need a resonant driver to make it work.
Isn't the piezo transducer alone enough for that? Simply generate a square wave signal of the same polarity as the measured current through the transducer, you get ZCS and automatic resonance tracking AFAICS (just need to get it going before the control loop can take over).
Ah, driving high frequency sonar transducers, been there done that.
The usual thing is to use a tuned transformer (Resonate the secondary winding inductance with the transducer fixed capacitance) as part of a fifth order or so matching network, then drive the whole thing with a square wave, the transducer will do a good job of turning it into a sine in the working fluid. Note that your driver will probably have to deal with a load that is not in fact resistive, active snubbers can be your friends.
These transformers can be small as the duty cycle is usually negligible, but the voltages can be huge so kapton tape is a good thing, as is litz wire to keep the Q where you want it.
Usually the input match is some form of L network, often with deliberate series resistance to make the bandwidth a little wider, do make sure you work from a G/B plot done in water, they measure **very** differently in air.
Are you sure that plot is impedance rather then admittance? I would expect the resonance to be a low impedance as the devices model as series resonant devices with an annoyingly large shunt cap and the acoustic radiation resistance in the series arm.
73 Dan.
Why not use a transformer?
because they are too bulky (?)
How small does it have to be?
A 700kHz transformer with a power rating of a few Watts, isn't very big.
Why not use a transformer?
because they are too bulky (?)
How small does it have to be?
A 700kHz transformer with a power rating of a few Watts, isn't very big.
In fact, how much you want to bet that a cheap 500khz-1Mhz 10 watt 12v wall-mount switching supply's tiny transformer could be used in reverse to drive the PZT.
Though I cant say anything about the efficiency...
Why not use a transformer?
because they are too bulky (?)
How small does it have to be?
A 700kHz transformer with a power rating of a few Watts, isn't very big.
In fact, how much you want to bet that a cheap 500khz-1Mhz 10 watt 12v wall-mount switching supply's tiny transformer could be used in reverse to drive the PZT.
Though I cant say anything about the efficiency...
It should work, but you might have to adjust the input voltage to give the correct output voltage.